1. Field of the Invention
This invention relates generally to data processing systems and more particularly to data processing systems in which peripheral subsystems are to be made available to more than one central processing unit and associated equipment. Apparatus is provided in the input/output multiplexer which permits the efficient transfer of information between more than one control interface units and the plurality of peripheral subsystems coupled to the input/output multiplexer.
2. Description of the Prior Art
It is generally known in the prior art to utilize an input/output multiplexer to provide an interface between the control interface unit of a data processing system and the peripheral subsystem. In the prior art, a peripheral subsystem will be available only to a single central processing unit. In the event that access to an input/output multiplexer and therefore to the associated peripheral subsystem by several control unit interfaces was desired, it was necessary to provide elaborate availability and decision-making apparatus to control the interchange of data signals. Features which have been considered in the design of such an interface include the present activity in the input/output multiplexer, priority of requests, period of waiting for transfer, etc.
It is therefore an object of the present invention to provide an improved data processing unit.
It is another object of the present invention to permit more than one central processing unit to have access to a peripheral subsystem.
It is a more particular object of the present invention to provide apparatus allowing more than one control interface unit to transfer data signals through the input part of an input/output multiplexer.
It is a still more particular object of the present invention to permit the transfer of data through the input part of an input/output multiplexer by alternating the availability of the input/output multiplexer to each of a plurality of control interface units.